Revision You asked to look at sliding filament theory… I feel we need to quickly start with muscle structure.

Voluntary /striated /skeletal muscle! Muscles are made up of bundles of muscle fibres Each fibre is a single muscle cell and can be several cms in length. (0.1mm in diameter) Bound together by connective tissue continuous with tendons. With a cell surface membrane: called sarcolemma Each cell is multinucleate: a single nucleus could not effectively control metabolism of such a long cell! Would take too long to move proteins. Striped: ability to contract Voluntary /striated /skeletal muscle!

One nuclei would be ineffective at controlling the cells metabolic process over such a long cell – e.g. if only one nuclei any enzymes needed for reactions produced in protein synthesis – would struggle to diffuse throughout the entire length of the cell Enzymes needed here also and in large quantities – but the further the distance the less reliable diffusion – the solution is to have more than one nuclei

Longitudinal Microscope picture of skeletal muscle

Muscle.... The muscle fibre contains sarcoplasm (cytoplasm) with numerous mitochondria Protein molecule: myoglobin Each muscle fibre is a bundle of smaller myofibrils arranged lengthways Each myofibril is made up of 2 kinds of protein myofilaments: actin (thin) and myosin (thick) These make up the contractile units called sarcomeres

Synoptic: Other pigments Myoglobin: Red pigment found in muscle cells. It doesn’t carry oxygen but it stores oxygen. It has got just one polypeptide chain, hence its dissociation curve’s shape. Has a greater affinity for oxygen

Are there any other key words you could include? Task In pairs: Put the words given to you in order to explain the structure of a voluntary muscle Are there any other key words you could include?

Muscle, made up of… Bundle of muscle fibres Muscle fibre is the cell Each muscle fibre is surrounded by the Sarcolemma Each muscle fibre is a bundle of Myofibrils (organelles) Myofibrils are made up of Myofilaments Actin Myosin Sarcomere The sarcomere is the smallest contractile unit of a muscle……………

The sarcomeres span from one Z line to the next.

Write bullet points to summarise your understanding at Watch animation https://www.youtube.com/watch?v=gZevEd0qeW4 Write bullet points to summarise your understanding at THIS STAGE

Muscle contraction: The contractile unit : the sarcomere is made up of 2 types of protein molecule: Actin: thin Myosin: Thick Contraction is bought about by the coordinated sliding of these proteins filaments within the sarcomere The proteins overlap=striated appearance. Actin only=light Actin+myosin=dark Myosin only =medium

The sarcomeres span from one Z line to the next. The Z lines are drawn closer in contraction as I band and H zone are reduced. A band does not change

(a) Diagram showing a section of myofibril to reveal sarcomere layout; (b) diagram showing the bands and zones present. (a)

DRAW THE BANDING PATTERN! Actin and myosin filaments in one sarcomere relaxed Z line The banding pattern of above The arrangement of the sarcomere when contracted DRAW THE BANDING PATTERN!

The central band of myosin alone has disappeared Either just actin or actin+myosin

The banded pattern shown in micrographs is due to the overlapping regions of the two types of fibre 18

In 1mm fibre=400 sarcomeres! Human thigh muscle=40 000 sarcomeres!

How the Sarcomere Shortens First watch this animation http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__sarcomere_contraction.html Bullet point your understanding

Actin Actin molecules are 2 strands made mainly of the protein actin (F actin) which are coiled around each other (twisted beads!) Associated with 2 other protein molecules: Tropomyosin: rod shaped protein that coils around the F actin, reinforcing it Troponin: these complexes made of 3 polypeptides are attached to each tropomyosin molecule ,one polypeptide binds to tropomyosin, one to the actin and one to calcium ions

Myosin: Myosin are the thick protein filaments Each myosin molecule consists of a tail and 2 protruding heads Myosin molecule heads protrude from the fibre When a muscle contracts it is the orientation of these that brings about the movement of actin Myosin heads attach to actin, dip forward and slide the actin over the myosin This is the sliding filament theory.

Myosin heads cannot bind to actin filaments troponin tropomyosin actin filament ADP myosin complex Pi myosin filament At rest, the actin-myosin binding site is blocked by tropomyosin, held in place by troponin Myosin heads cannot bind to actin filaments

A nerve impulse arrives at the neuromuscular junction Calcium ions are released from the sarcoplasm reticulum (specialised ER) Diffuse through the sarcoplasm Bind to troponin molecule Initiates the moving of the myofilaments: actin and myosin.

Ca2+ binds to troponin, changing its shape Tropomyosin is pulled out of the binding site: shifts position and exposes myosin binding site Myosin head can bind – bond is actin-myosin cross bridge

When myosin binds to actin stimulates ATPase, breaking down ATP to ADP + Pi Energy provided changes myosin head to nod forward, pulling actin filament along in a ratchet motion over myosin This is the power stroke, ATP is used

Free ATP binds to myosin head Actin-myosin cross bridge breaks: myosin head detaches ATP is hydrolysed, and myosin head returns to original upright shape

With continued stimulation the cycle is repeated The collective bending of many myosin heads combines to move the actin filaments relative to the myosin= muscle contraction

If stimulation ceases, Ca2+ is actively pumped back into sarcoplasmic reticulum (needs ATP) Troponin and tropomyosin return to original positions Muscle fibre is relaxed

Task: 10 minutes http://media.pearsoncmg.com/intl/snab_2009/topic_7/interactives/7_2/topic_7_2.html Watch Then use your understanding to put the statements in order to describe the steps that must occur to bring about contraction of a sarcomere

Write bullet points to summarise your understanding at Watch animation again? http://www.wellcome.ac.uk/Education-resources/Teaching-and-education/Big-Picture/All-issues/Exercise-energy-and-movement/WTDV033020.htm Write bullet points to summarise your understanding at THIS STAGE

Please get out your 4 questions for homework to hand in Starter: 10 minutes Please get out your 4 questions for homework to hand in Watch: Fantastic 4 minutes https://www.youtube.com/watch?v=BMT4PtXRCVA Get out your sheet you were completing on sliding filament theory and mark I am going to give you some questions/mark schemes I had copied that we had not used, they are for your own practice We will complete the last bit on muscles……

Learning outcomes: Explain, with diagrams and photographs how muscles contract in terms of the sliding filament theory. Outline the role of ATP in muscular contraction and how the supply of ATP is maintained in muscles

Homework 1 Collate diagrams and photographs to explain the sliding filament theory. Annotate these diagrams to show your understanding. Include voluntary muscle structure, sarcomere etc. Extension: 2 good biological sciences review articles on muscle on my website.

The role of ATP List the stages where ATP is involved in muscle contraction 3 marks In the power stroke: when the myosin head attaches to actin binding site and bends energy is required Energy is required to break this cross bridge and for the myosin head to go back to its original position When contraction finishes to pump calcium ions back into sarcoplasmic reticulum

Maintenance of the ATP supply There is only enough ATP to provide 1-2 seconds worth of contraction So ATP must be regenerated as quickly as it is used There are 3 mechanisms for this:

Three energy systems summary: Cells cannot store much ATP At start of exercise immediate recharge of ATP is made using creatine phosphate Stored in muscle cell sarcoplasm and can be hydrolysed to release energy Energy is used to regenerate ATP from ADP and Pi. Creatine phosphate provides the Pi Creatine phosphate creatine + Pi ADP + Pi ATP Creatine phosphate + ADP creatine + ATP No oxygen needed Provide energy for 6-10 seconds Known as the ATP/CP system

During exercise Energy first supplied by ATP/PC system Anaerobic respiration: in muscle cell sarcoplasm. Quick but produces lactate which is toxic. Lactate enters blood where it leads to stimulation of more blood to the muscles Aerobic respiration in muscle cell mitochondria can regenerate ATP as quickly as it is broken down if there is sufficient supply of oxygen and respiratory substrate to the muscles Allows exercise to be sustained.

Suggest which process for ATP regeneration is most important for Quick question Suggest which process for ATP regeneration is most important for A marathon runner 100m sprinter?

Plenary exam question 8 marks = 8 minutes Independently complete the examination question….. WWW/EBI? Extension: Question 2 9 marks

Test Biotechnology Please reflect on your test result One person got their TG Most others were the grade below, so generally good Lack of revision/understanding evident in some areas?? Exam technique: read the questions more carefully… Your Mock??